Windmill or Wind Turbine- powered boats: how many are out there, and are they viable?

Hey Rick;
I keep reading about people refering to your website. But I don´t see it anywhere. Could you list it for me and others.
Thanks, Richard Miller

 

Richard
It is shown in my public profile on this forum.

You will be disappointed I fear. It is just a PowerPoint presentation converted to html so quite clunky. I originally started the site so I could refer to images and videos for sites that do not allow these to be posted. It has some video links embedded and these are quite interesting - at least I think so.

I have heaps more stuff on high efficiency boats that is not covered on the site.

I have attached the latest iteration of the Solar-Wind boat. Sill no windows in this one! It now has the detail design of the propulsion leg and just the mock up of the wind turbine. I have the generator and controller on order for the turbine so I will be making my own rather than buying. It is identical to the water prop drive so I can generate or propel from either unit.

I have also almost decided that I will not use a steering vane on the turbine. I think I will have direction electrically controlled so I can feather it easily.

Rick W.

 

Hi Rick,
I imagine the long vertical shaft for the prop would need to be strong. If you damage the prop on something hard during a heavy sea, how would you deal with that?

 

The blades are around 12mm thick and each 1.1m long. Not much projected area when feathered side-on to the prevailing wind. That is one reason for not having it weather vane. If the rotation is powered I can just turn it side on to wind. I will also have enough grunt in the motor/generator to stall the prop in gale force winds - not that I want to test this.

The boat will be on its ear before the turbine pole fails - same as any mast only my righting moment with 250kg of ballast on a 1.5m WL beam is much less than your typical deep keel yacht. The whole boat has relatively low forces compared with a yacht - even catamaran or trimaran.

The turbine is only schematic at this stage. The actual rotor will be carried on a ZP2 right angle drive with a shaft to a Mars BLDC motor/generator mounted down on the deck. This keeps the heaviest bit low down. The whole thing will weigh around 18kg so will be removed for trailering.

Rick W.

 

Sorry Rick, I should have been more specific.....my question was referring to the underwater prop

 

The shaft leg will be designed to fail before it damages the hull. The prop is the most exposed and it will have a slipping clutch to protect it. The banging noise should be a dead giveaway that I am in strife.

I will be able to lift the leg out to inspect but if it is bent I will not be able to repair it. At that point I will need to switch to air propulsion. This is not as effective as the water prop but will still easily push along at 6 knots.

I also intend to carry a pedal drive for some sort of small shore boat. The pedal drive will slot into the drive well in the boat so I then use the high calorie burn 120W engine - I already have really nice parts for this. The pedal drive will push the boat at about 3.3 knots so I can make way under an absolute emergency.

There are not many boats with triple redundancy with their propulsion system.

Rick W.

 

LOL I have nice legs too. I do a bit of cycling.

Actually, my boat has triple redundancy if you include the oars (and the miserable oarsmen). I was thinking of asking you if I could by one of your short wide pedal boats to store on my cat....but then I opted for 2 waveskis joined with removable beams.....a great little taxi and some fun in the surf.

6 knots with air propulsion alone....wow...that's good.

 

In very strong wind, it would be interesting to see how fast the boat will go, with the propellor up out of the water....could be an option when the batteries are full.

 

This a a long thread and I think I have dutifully read it all. Initially I had no trouble with the idea that a wind turbine can provide enough power to a water propeller to drive a boat directly into the wind. I reasoned that the turbine is merely a rotary sail and the propeller blade is in effect a rotary keel. With sufficiently low gearing it will obviously work in a land vehicle and translating the idea to a water vehicle merely adds hydrodynamic drag and propeller slip and eliminates static friction. The idea that the concept can achieve a hull speed in excess of the wind speed is, however, a little harder to accept. Sounds like a violation of some physical law or two. I haven't seen a satisfying analysis and I need the reassurance of math so I decided to try it myself. As I am neither a mathematician, an aerodynamicist or a hydrodynamicist I can only go on logic and hope I got it right. Forgive me if I didn't.

This is a junior high school level mathematical treatment of a wind turbine-powered boat. I have tried to make it rigorous but at the same time, simple. For clarity I use caps for properties, lower case for physical objects possessing those properties.

Using lower case letters for the physical objects, let h = hull, w = wind, p = (water) prop, t = (wind) turbine, g = geartrain

Using caps for the physical properties, let S = speed, F = force, E = efficiency, R = resistance, P = power, A = area, Q = acceleration

-thus Qh represents the acceleration of the hull, Sw represents wind speed and so forth. Assuming zero wind force on the hull:

Force balance equation:
Fp - Qh.Mh - Ft - Rh = 0

Steady state (Qh = 0) case:
Fp = Ft + Rh

Power equation:
Ft.Et.Eg.Ep.(Sw + Sh) = (power available from prop) = Fp.Sh

For perfect efficiency:
Et = Eg = Ep = 1

Revised power equation:
Ft.(Sw + Sh) = Fp.Sh

Expand power equation:
Ft.Sw + Ft.Sh = Fp.Sh

Substitute for Fp:
Ft.Sw + Ft.Sh = Ft.Sh + Rh.Sh

- which reduces to:
Ft.Sw = Rh.Sh

I.e., in steady state with 100% efficiency turbine power must equal hull hydrodynamic losses.

Note: the equations all comply with Newton's laws of motion and the law of conservation of energy. The last equation allows the possibility of moving upwind with a turbine/geartrain/propeller arrangement, and even of the hull speed exceeding wind speed - counter-intuitive though that seems to me. Whether these things are achieveable will depend on the overall efficiency and the relationship of Rh (hull hydrodynamic resistance) and Ft (air force on turbine ) to wind and hull speeds. The whole business is complicated by the fact that the relationships are not linear.

Let's put the efficiencies back into the equation but assme that they are constant. This implies they are independent of speed, an unlikely assumption in the case of propeller slip but a reasonable simplification. The function Ft represents the relationship of turbine force on apparent wind speed.

Original power equation:
Ft.Et.Eg.Ep.(Sw + Sh) = Fp.Sh

substituting Ft:
Ft[Sw + Sh].Et.Eg.Ep.(Sw + Sh) = Fp.Sh

I want to express Fp as a function of something already in the equation. Propeller force is a function of propeller slippage which for constant propeller efficiency is proportional to hull speed:

I have:
Sh = (prop revs) x (prop pitch) x Ep

but:
(prop slippage) = (prop revs) x (prop pitch) - Sh = Sh (1-Ep)/Ep = Sh x constant

So prop thrust can be expressed as a function of hull speed, thus:
Fp = Fp(Sh)

substituting Fp[Sh]:
Ft[Sw + Sh].Et.Eg.Ep.(Sw + Sh) = Fp[Sh].Sh

This is still the simple power equation from before, I have merely show the propeller force (thrust) and turbine force (drag) as dependent on the values of wind speed and apparent wind speed respectively. However, it may be time to graduate from junior high school. As a fluid moves past an object (or vice versa) several types of flow occur. The fluid slides past the skin of the object in laminar flow, it has to shift over to get out of the way and back again after it has passed, it may or may not experience turbulence if speed is sufficient, and it may even experience sonic shock if speed exceeds that of sound in the fluid.

Lets assume the forces resulting from these are all negligible at the speeds relevant to a wind turbine-powered boat except the second, in which the fluid moves around the object.

An object of area A moving at speed S through a fluid displaces a volume equal to A.S
The mass of this quantity of fluid is A.D.S where D is the fluid density
This mass must be accelerated, mostly sideways at a rate proportional to S; lets call it 0.5C.S
C is a constant known as the drag coefficient which depends on the shape of the object. The value of C is about 1 for a brick, around 0.3 for a modern car and around 0.03 for an aircraft.

From Newton's laws of motion the force required for the acceleration is given by:

The drag equation:
F = 0.5C.A.D.S(squared)

Using this formula to replace the functions in the last version of the power equation above using constant K to simplify it, we get:
Kt.(Sw + Sh)cubed.Et.Eg.Ep = Kp.(Sh)cubed

This suggests that hull speed will vary as wind speed up to the point where the assumptions made above come back to bite my ***. I doubt it will be the one about sonic shock but the one about turbulence and the one I forgot (wave drag) are also going to muscle into the act. The lesson I am learning from all of this however, is a simple one: there seems to be no theoretical reason why the hull speed of a wind turbine-powered boat cannot exceed the wind speed, although the practical reasons may be something else.

Over to the experts now. I expect to get shot down in glorious flames not once but several times over but it was a nice flight while it lasted.

 

AK
I did not go completely through the analysis but it looks right. I agree with the conclusion.

I would like to give you some basic performance numbers to compare your realistic performance with what I have done.

The turbine operates at 90% efficiency through the range of interest and has a design point of 5kW at 10m/s wind. This means that 90% of the work done on the turbine as it passes through the air is recoverable. The rest of the energy is lost in parasitic drag. The power v wind speed relationship is cubed.

The boat has negligible wave drag, being long and slender, but viscous drag costs 1kW at 5m/s and is also a cubed relationship with boat speed. The boat is very low and streamline so the windage, other than the turbine force, is negligible.

The prop has an efficiency of 88% thoughout the speed of interest.

The turbine and prop are continuously optimally geared with a CVT having a mechanical efficiency of 95%.

What speed will the boat do directly into the wind when wind speed over the water is 8m/s.

Rick W.

 

God boy Rick! Further to this: An aircraft variable pitch propellor only needs to be spinning at half speed or less to make an acceptable Rotary Sail. This means QUIET and UNOBTRUSIVE POWER to a standard marine propellor. I was sorry to see the NZ Rotary Sail was onlya flash copy of Jims Bates' original effort which is very basic and inefficient. The Rotary Sail removes all hull limitations to apparent wind speed and only needs a pitch control for any wind strength. Cheers, Lin.

 

Can anyone give me a crude estimation on how big a windturbine would need to be, to give similar driving force to a bermudan rig with 380 ft2 sail area?

I'm talking about pure air power...no motors, no batteries, no underwater propellors etc.

 

Will not work without a propeller.

Rick W.

 

Dammit....have I just made a fool of myself? I always had trouble visualising how the windturbine could act like a spinnaker (as mentioned by someone in this thread).

Hi Rick.

By this do you mean you would use the motor to power the windturbine, effectively turning the boat into an airboat?

 

Point 1:

A fast-spinning rotor not connected to a propeller acts very well as a spinnaker and also on the other courses available for normal sailing (think how an autogiro (gyrocopter) works). Lord Brabazon built a boat that worked this way in the 1930s (as everybody knows). The boat a - "Solent Redwing" has been restored and has been sailed recently.

Point two.
I don't want to rain on anyones parade, but a statement by Rick Willoughby interested me: "I do not have to worry about tacking as it will go directly to windward."
Do you know this Rick?
Have you tested the idea in real life? Maybe you have made a model that demonstrates it?
From the parameters I have gleaned from the description of the system, I don't feel that it will go directly to windward, or if it does, only very poorly. In fact, I have never heard of a windturbine boat with electric drive going directly to windward in the whole world. If i'm wrong please direct me to where it has occurred.
Mechanical drive is more plausible, because there are no losses. I've done a few tests myself, so I know a little about it.